1. Field of the Invention
This invention relates to an impact-driven rotating device such as an impact wrench and an impact screwdriver for tightening or loosening a bolt, a nut, a screw or the like.
2. Description of Related Art
An impact-driven rotating device is used for tightening or loosening a nut, a bolt, a screw or the like (hereinafter may simply referred to as xe2x80x9cnut or the likexe2x80x9d). The output shaft of the impact-driven rotating device is rotated by imparting hitting force against the output shaft using a rotatably driven hammer. This kind of impact-driven rotating device can obtain a higher tightening torque than a regular rotating device in which an output shaft thereof is directly rotated by a speed-reduction output of a motor. However, in tightening a small nut or the like, the impact-driven rotating device may cause damage thereto when too much tightening occurs. On the other hand, an operation for avoiding such damage may lead to insufficient tightening torque.
Therefore, in a conventional impact-driven rotating device, in order to control the tightening torque, the number of hitting impacts of the output shaft by a hammer is counted, and the motor is stopped when the number reaches a predetermined value by assuming that a nut or the like is tightened at a predetermined tightening torque. This utilizes the fact that tightening torque is in proportion to a square root of the number of hitting impacts.
In the aforementioned conventional impact-driven rotating device, it is assumed that no hitting impact occurs until a nut of the like comes into contact with an object. However, in a case where a coated bolt is tightened, or a member to be tightened causes a number of hitting impacts until it comes into contact with an object, it is impossible to stop the tightening operation at appropriate tightening torque.
An object of the present invention is to provide an impact-driven rotating device which is capable of tightening a member at predetermined tightening torque.
According to a first aspect of the present invention, an impact-driven rotating device includes an output shaft, a hammer for rotating the output shaft by imparting impact to the output shaft, and a rotation driver for rotating the hammer. The impact-driven rotating device further includes an impact detector, a rotation angle detector, a rotation speed detector, an energy calculator, a between-impacts rotation angle calculator, a tightening torque calculator, and a controller. The impact detector detects the impact imparted by the hammer. The rotation angle detector detects a rotation angle of the output shaft. The rotation speed detector detects a rotation speed of the output shaft from the rotation angle detected by the rotation angle detector. The energy calculator calculates energy imparted to the output shaft from the rotation speed detected by the rotation speed detector. The between-impacts rotation angle calculator calculates a rotation angle of the output shaft rotated within a time interval from a detection of a previous impact to that of a subsequent impact by the impact detector from the rotation angle detected by the rotation angle detector. The tightening torque calculator calculates tightening torque by dividing the energy calculated by the energy calculator by the rotation angle calculated by the between-impacts rotation angle calculator. The controller stops the rotation driver when the tightening torque calculated by the tightening torque calculator becomes equal to, or greater than, a predetermined value.
The energy imparted to the output shaft by hitting the shaft by a hammer is generally equal to the energy to be consumed for tightening a member. Therefore, in the aforementioned impact-driven rotating device, the energy calculator calculates the energy imparted to the output shaft from the rotation speed detected by the rotation speed detector, and the tightening torque calculator calculates the tightening torque by dividing the energy calculated by the energy calculator by the rotation angle calculated by the between-impacts rotation angle calculator. Accordingly, the accuracy of detecting the tightening torque can be enhanced, resulting in an appropriate tightening operation with predetermined tightening torque.
In the aforementioned impact-driven rotating device according to the first aspect of the present invention, it is preferable that the rotation driver includes a driver main body having a drive shaft and a reducer for transmitting a rotation of the drive shaft to the hammer at a predetermined reduction ratio, wherein the rotation angle detector includes a drive shaft rotation angle detector for detecting a rotation angle of the drive shaft to detect the rotation angle of the output shaft from the detected value detected by the drive shaft rotation angle detector, and wherein the between-impacts rotation angle calculator calculates a rotation angle of the driving shaft rotated within a time interval from a detection of a previous impact to that of a subsequent impact by the impact detector from the detected value detected by the driving shaft rotation angle detector, and calculates the rotation angle of the output shaft by subtracting the rotational angle difference between the rotation angle of the hammer and that of the output shaft generated each impact of the output shaft from the value obtained by dividing the rotation angle detected by the driving shaft rotation angle detector by the reduction ratio of the reducer.
With this impact-driven rotating device, there is no need to attach the rotation angle detector to the output shaft in order to detect the rotation angle of the output shaft which is easily affected by oil, dust or the like, resulting in enhanced reliability of the calculated tightening torque.
In the aforementioned impact-driven rotating device according to the first aspect of the present invention, it is preferable that the impact-driven rotating device further includes an impact number counter, wherein the impact number counter counts the number of impacts caused by hitting the output shaft by the hammer after the rotation angle calculated by the between-impacts rotation angle calculator becomes smaller than a predetermined threshold value, and wherein the tightening torque calculator calculates a tightening torque by multiplying a square root of the number of impacts counted by the impact number counter by a proportional coefficient determined in accordance with a member to be tightened.
When the rotation angle calculated by the between-impacts rotation angle calculator becomes smaller than a predetermined threshold value, it becomes impossible to neglect an error of the detected rotation angle or an error resulting from the division of the energy by the detected rotation angle. However, in the impact-driven rotating device, since the tightening torque calculator calculates tightening torque by multiplying a square root of the number of impacts counted by the impact number counter by a proportional coefficient, an error of the detected rotation angle in a high-torque region where the rotation angle of the output shaft is small or an effect of an error resulting from the division of the energy by the rotation angle can be avoided. This enhances the accuracy of detecting a tightening torque.
In a case where the energy imparted to the output shaft every impacts is constant, the rotation speed calculator can be omitted. Therefore, according to the second aspect of the present invention, an impact-driven rotating device includes an output shaft, a hammer for rotating the output shaft by imparting impact to the output shaft, a rotation driver for rotating the hammer, an impact detector for detecting the impact imparted by the hammer, a rotation angle detector for detecting a rotation angle of the output shaft, a between-impacts rotation angle calculator for calculating a rotation angle of the output shaft rotated between a detection of a previous impact and that of a subsequent impact by the impact detector from the rotation angle detected by the rotation angle detector, a tightening torque calculator for calculating tightening torque by dividing the energy calculated by the energy calculator by the rotation angle calculated by the between-impacts rotation angle calculator, and a controller for stopping the rotation driver when the tightening torque calculated by the tightening torque calculator becomes equal to, or greater than, a predetermined value.
Other objects and advantages of the present invention will become apparent from the description of the preferred embodiments, which may be modified in any manner without departing from the scope and spirit of the present invention.